1. Field of the Invention
This invention relates to electronic angle of advance correction for a controlled-ignition internal combustion engine in response to pinging or knocking and engine charge.
2. Description of the Prior Art and Related Patent Applications
Improvement of the automotive combustion cycle has always been a concern of the motor mechanic and was one of the guiding elements in the modification of combustion chamber architecture and the increase in the compression rate. Indeed, this latter parameter directly conditions the engine's thermodynamic efficiency. Unfortunately, the increase in the compression rate shifts the zone where the pinging appears towards the peak of the torque curve applied to the engine as a function of the angle of advance, and if the engine's compression rate continues to be raised, the advance protection clearance in relation to the pinging causes the engine to operate with characteristics which penalize it more than with a lower compression rate. Nonetheless, it may be worthwhile to make use of engines with high compression rates, in particular to improve the combustion efficiency in partial charges. To this end, if it is desired to keep an engine with acceptable acceleration performances, it should not be penalized in its transitional phases, and it should be protected from the appearance of pinging when it operates in a stabilized phase.
Various devices for protecting an engine from pinging are known to the technician. These involve either increasing the richness of the mixture or reducing the advance. The first solution is implicitly achieved in the fuel-mixing device by means of an accelerator pump which enriches the mixture in acceleration phases and with the carburetor's compensating devices acting in the vicinity of the full charge, which also enrich the mixture; the second solution is really only effective when the engine is operating at a stabilized rate.
In related commonly owned U.S. patent application Ser. No. 141,147 filed Apr. 17, 1980 and relating to a "Process and System for Computation and Adjustment of Optimum Ignition Advance," there is disclosed a process according to an initial aspect of the invention for calculating and adjusting the optimization of the advance in an internal combustion engine by means of a system for detecting pinging with the aid of a transducer, such as an accelerometer rigidly attached to the engine's cylinder head. This process is noteworthy in that the accelerometric signal is treated in analog form, including in particular the integration of the signal inside a given window; the resulting signal converted to numerical form; an average value C calculated proportional to the preceding n pings; two thresholds of comparison S.sub.1 and S.sub.2 calculated which are each a linear function of the average value C calculated previously; the numerically integrated accelerometric value compared to each of these thresholds, and from them the deduction of the presence or absence of an audible pre-ping and/or ping value which is then used to act on the programmed advance of the electronic ignition. In the same patent application, and according to a second aspect of the invention, there is disclosed a system for calculating and adjusting the optimization of the advance in an internal combustion engine by means of a system for detecting pinging by means of a transducer such as an accelerometer rigidly attached to the engine's cylinder head. This system is noteworthy in that it includes means for analog processing of the signal taken from the accelerometer, including in particular an integrator, logical integrator control means, an analog-digital converter, and a micro-computer including in particular a sequencer, a stage for calculating an average value C proportional to the preceding n pings, two stages for calculating comparison thresholds (S.sub.1, S.sub.2) which are each a linear function of the average value C previously calculated, and means for deducing the existence or absence of an audible pre-ping and/or ping value.
In this previous device, the utilization of an average value for n pings takes up a good deal of space in the micro-computer's memory. Studies pursued since the filing of this first application have shown that the average value C can be calculated by taking into account the preceding average value affected by a multiplier coefficient k and by taking into account the new measured value, and that it is not absolutely necessary to calculate two ping thresholds, the use of a "pre-ping threshold" being non-essential. However, the cylinders are treated successively one by one for detection, and the average value C is calculated from the data relating to a given cylinder at a given moment. There are thus as many average values as there are cylinders. It is therefore preferable to calculate only one ping threshold and to take into account data relating to the engine charge in order to determine the strategies for shifting the advance.